2018  10.5
2017  9.6
2016  9.5
2015  9.9
2014  10.3
2013  8.7
2012  9.1
2011  9.6
2010  7.6 
2009  9.2
2008  9.5
2007  9.9
2006  9.5
2005  9.0
2004  8.9
2003  9.4
2002  9.6
2001  9.0
2000  9.9
1999  9.5
1998  9.1
1997  8.9
1996  7.2
1995  8.9
1994  9.7
1993  8.5
1992  9.4
1991  8.4
1990  9.5
1989  9.5
1988  9.1
1987  7.4
1986  7.9
1985  7.4
1984  8.0
1983  9.0
1982  8.9
1981  8.2
1980  7.6
1979  7.7
1978  7.8
1977  8.7
1976  8.5
1975  8.9
1974  8.8
1973  8.2
1972  7.8
1971  8.4
1970  7.7
1969  7.8
1968  8.2
1967  8.9
1966  8.5
1965  7.5
1964  8.1
1963  7.1
1962  7.1
1961  9.0
1960  8.4